With advantages such as simple implementation, robustness against frequency selective fading, and support for multi-antenna technique, etc., Orthogonal Frequency Division Multiplexing (OFDM) has become an effective technique supporting high-speed wireless communication. However, OFDM has the drawback of high envelope fluctuations during signal transmission, thus the power efficiency of OFDM is limited, especially when OFDM is applied in uplinks in wireless communication system. The Single Carrier-Frequency Division Multiple Access (SC-FDMA) technique put forth in recent years has overcome the drawback of high envelope fluctuations during signal transmission of OFDM, and can be implemented by means of DFTS (Discrete Fourier Transform Spreading)-OFDM. Therefore, SC-FDMA becomes a key technique for uplinks in wireless communication.
In a SC-FDMA system based on DFTS-OFDM, the transmitted data vector of each user is pre-coded with DFT matrix before it is mapped to the sub-carrier of OFDM system. The resultant transmitted signals all have lower envelope fluctuation, no matter they are measured with Peak to Average Power Ratio (PAPR) or Cubic Metric (CM). Therefore, higher power efficiency and signal coverage can be obtained in the uplink. At the receiving end of the system, the inter-symbol interference caused by frequency selective fading channel can be suppressed by frequency domain equalization with low complexity. The envelope fluctuation of transmitted signals can be further reduced by frequency domain pulse shaping. In conventional single carrier transmission, though the envelope fluctuation of transmitted signals can be reduced with increase of the roll-off factor of pulse shaping, the spectral efficiency loses at the same time. The object of the present invention is to reduce envelope fluctuation of transmitted signals without loss of spectral efficiency.
In frequency selectivity channels, OQAM (Offset Quadrature Amplitude Modulation)-OFDM transmission usually loses its orthogonality; as a result, the influence of inter-channel interference (ICI) and inter-symbol interference (ISI) has to be eliminated with a more complex equalization method at the receiving end. That drawback hampers the application of OQAM-OFDM in actual systems. An essential idea of the present invention is to introduce a cyclic prefix (CP) into OQAM-OFDM transmission, to obtain an equalization method with low complexity by utilizing the block transmission and cyclic convolution features of cyclic prefix.